1. Field of the Invention
The present invention relates generally to a security monitor system which employs one more video cameras for monitoring an area which will be hereafter referred to as, a "monitoring area". More specifically, the invention relates to a security monitor system employing a plurality of video cameras for monitoring a plurality of monitoring areas.
2. Description of the Background Art
In recent years, there have been proposed various security monitor systems. Some of these conventional security monitor systems employ video cameras for monitoring the monitoring areas. Video signals are usually reproduced on video monitors for allowing visual monitoring at a place remote from the monitoring areas. Alternatively, the video signals may be recorded with video tape recorders (VTR's).
Conventionally, the video cameras are connected to respectively corresponding video monitors through independent signal lines for monitoring a plurality of monitoring areas. This requires a number of video monitors that corresponds to the number of video signals thus incurring substantial cost. In some of the more recently developed systems, attempts have been made to reduce the cost of such security monitor systems by providing a common video monitor which can receive video signals from a plurality of video cameras. In such case, the video signals from different video cameras are switched in a time-sharing manner or by a manual switching operation. However, even with such systems, the video cameras have to be connected to the common video monitor via mutually independent signal lines. Therefore, the number and length of the signal lines keep the costs high. In addition, proper adjustment of the switching timing is difficult to determine, since the switching intervals should not be too long to allow monitoring of all of the respective areas within a resonable period, but the period in which the picture of one monitoring area is displayed should be long enough to visually monitor movement occurring in the picture at the corresponding monitoring area.
Furthermore, when the video signals from a plurality of video cameras are to be recorded by means of a common VTR, the obtained information is not complete for any of monitoring area.